In semiconductor manufacturing apparatuses and liquid crystal manufacturing apparatuses, demand for linear motors has been increasing as driving sources of positioning apparatuses adapted to carry out positioning of works loaded thereon. However, a coil is essential to the linear motor and it cannot be avoided that the coil acts as a heat generation source. Accordingly, a cooling structure for the coil is essential to the linear motor for use in an apparatus that requires strict temperature control, such as, for example, a stepper. The linear motor having the coil cooling structure is called a cooling-type linear motor and disclosed, for example, in Japanese Unexamined Patent Application Publication (JP-A) No. 2001-275337.
Generally, cooling-type linear motors are often of the type that covers a coil with a casing of metal, resin, or the like so as to define a space around the coil and cools the coil by feeding a coolant to the inside of the casing. The casing is attached with a terminal block having one or more terminals for connection between the inner coil and an external circuit. Issues to be solved in the linear motor of such a type are how to seal the terminal block, how to improve its maintenance, and how to attach it at a low cost.
Description will be made about first to third examples of terminal block structures in conventional cooling-type linear motors. In any of the first to third examples, the main part of a terminal block except terminals is made of an insulating resin material.
The first example uses a commercial terminal block 100 as shown in FIG. 1. The terminal block 100 is provided at its upper portion with a plurality of terminals 110 for external connection and at its lower portion with a plurality of metal terminals 111 connected to the terminals 110. Terminals 113 are connected to the metal terminals 111. This is because the length of the metal terminal 111 of the commercial terminal block 100 is short. The terminal block 100 is fixed to a casing 200 of the linear motor through a non-illustrated board or adhesive resin material. The casing 200 is formed with through-holes 201 for passing the terminals 113 therethrough. Passing portions of the terminals 113 in the casing 200 are sealed with seal portions 210 using glass, epoxy resin, or the like. Such a seal structure is called a hermetic type. Each terminal 113 is provided, at its portion corresponding to the seal portion 210, with a slip-off preventing portion 112 having an increased diameter. In the casing 200, the terminals 113 or lead wires connected thereto are connected to a non-illustrated coil of the linear motor.
The second example shown in FIG. 2 also uses, like in FIG. 1, a commercial terminal block 100 having terminals 110 and metal terminals 111. The terminal block 100 is fixed to a casing 200 of the linear motor through an adhesive resin material (not shown) or an O-ring 120. In the case of using the O-ring 120, the casing 200 is formed with an annular groove 202 for receiving the O-ring 120 therein. The metal terminals 111 are connected to lead wires 121, while the lead wires 121 are connected to coil-side lead wires 220 brought out from the casing 200. The lead wires 121 and the coil-side lead wires 220 pass through through-holes 201 so as to be received in the casing. In the case of using the O-ring 120, the terminal block 100 is attached to the casing 200 by the use of a plurality of bolts 130.
The third example shown in FIG. 3 also uses, like in FIG. 1, a commercial terminal block 100 having terminals 110 and metal terminals 111. The third example has a structure where a plate 150 made of a metal material is interposed between the terminal block 100 and the casing 200 in the second example. The plate 150 has through-holes (not shown) for passing lead wires 121 therethrough. Adhesive is used for bonding between a lower surface of the terminal block 100 and the plate 150, while an O-ring 120 is used for sealing between the plate 150 and the casing 200. The terminal block 100 is, along with the plate 150, fixed to the casing 200 by the use of a plurality of bolts 130.
In the case of the foregoing first example, the secure sealing can be expected since the hermetic-type seal structure is employed. However, the hermetic-type seal structure is high in cost. Further, the terminal block 100 is difficult to detach once it has been fixed and, therefore, there is a problem in its maintenance.
In the second and third examples, there is a merit that the structure itself is simple, resulting in low cost. However, in the case of using the O-ring 120 in the second example, a coolant in the casing 200 may leak from the terminal block 100 itself. This is caused by incompleteness of the sealing performance of the terminal block 100 itself. Even in the case of using the adhesive in the second example, there is a problem that the sufficient sealing performance cannot be obtained due to thinness of an adhesive layer (smallness in bonding area).
Further, any of the first to third examples has a problem that reliability is very low in terms of electrical insulation. In addition, the resin terminal block and the metal largely differ in linear expansion coefficient. In the seal structure between those having different linear expansion coefficients, there is a problem that the sealing performance is degraded due to thermal deformation.
Therefore, it is an object of this invention to provide a waterproof terminal block unit having high electrical insulation performance.